It is well known to use large vessels, moored to the sea bed, serving for example as a floating FPSO vessel for Production, Storage and Off-loading of hydrocarbons offshore. Such vessel may be moored by means of a turret system, allowing the FPSO to weathervane, dependent upon the direction of waves, wind or currents. Alternatively such vessel may use a mooring system consisting of a large number of mooring lines, arranged in a catenary spread.
WO 2005/118389 describes a method for dynamic positioning of a vessel, wherein a positioning system controls at least one positioning machinery, and where two or more buoys, each comprising at least one positioning machinery are coupled to the vessel.
US 2008070456 describes a method of dynamic positioning of a vessel, wherein a positioning system controls at least one positioning machinery, and where two or more buoys, each comprising at least one positioning machinery, are coupled to the vessel.
WO 2004/074085 describes a device for loading and unloading a vessel, wherein a loading pipe or a loading hose is connected to the vessel via a floating, self-moored coupling unit designed to be moored to the vessel, preferably near the manifold of the vessel. The coupling unit has sufficient propulsive capacity to maintain the vessels position during the loading operation.
WO 00/27692 describes a device for positioning of vessels, such as ships, barges, semi-submersibles or the like, during operations, such as drilling, production or geological operations. The device consists of a single floating structure whose vertical position in the sea can be regulated and is anchored to the sea bed via a number of anchoring lines.
Problems associated with prior art solutions are limited capacity with turret/swivel system (ref. weathervaning); line interference due to the use of a large number of lines into congested area (mooring, umbilicals, power cables, risers); and high capital investment costs
Further, it should be appreciated that existing disconnectable systems have less capacity than permanent turret moored systems.